Studies of the rates of renaturation of mitochondrial DNAs (mtDNAs) from a number of phylogenetically diverse animals and plants will be made in an attempt to define the unique nucleotide sequence lengths of these DNAs and therefore the amount of genetic information which each can carry. Sequence homologies in mtDNAs of phylogenetically diverse organisms will be tested for using qualitative and quantitative hybridization techniques. Kinetoplast DNA (kDNA) of Crithidia (protozoa) has a complex form. The basic molecule is a 0.8 micron circle. Up to 46 circles are topologically interlocked into a group. Groups of circles are topologically interlocked into large associations. The renaturation kinetics of purified circular kDNA of different species of Crithidia and of the related Trypanosoma will be studied to try to establish all of the circles of a species carry the same genetic information. The extent of nucleotide sequence homologies between different species will be examined by hybridization studies. Density labeling, autoradiography and electron microscopy will be employed to try to determine whether kDNA doubling involves replication of every circle or sequential replication of a few circles. Electron microscope autoradiography will be used to try to gain information concerning the pattern of kDNA synthesis in situ.